Re: 1980s 18hp mercury running lumpy
There are lots of different things to check/adjust. It would help if you could say what had already been tried.<br /><br />However, as a first line of attack you might try new plugs (cheap/easy) and set them correctly. Check the plug leads and caps are good and corrosion free.<br /><br />Check engine temperature - A couple of engines I've had with thermostats stuck open or missing had strange behaviour and didn't run well particulary at idle.<br /><br />Also another quick/easy check is compression. If the cylinders are way different to each other it could be that.
